Ecotoxicological assessment of the impact of paper and pulp effluent on the lower Thukela River catchment, KwaZulu-Natal, South Africa and the toxicological assessment of similar effluent from two other mills

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Ecotoxicological assessment of the impact of paper and pulp effluent on the lower Thukela River catchment, KwaZulu-Natal, South Africa and the toxicological assessment of similar effluent from two other mills

Abstract:

The lower Thukela River catchment supports the highly industrialised
Mandini/Sundumbili Industrial Complex, which in turn supports Tugela Rail, a textile
factory, a vegetable-oil factory, as well as the Sundumbili Sewerage Treatment works.
All of these industries release their wastes into the Mandini River that leads into the
lower Thukela River. Another major potential impacting factor on the lower Thukela
River is the Sappi Tugela pulp and paper mill that has both abstraction and discharge
points in the same region. In 2004 the Department of Water Affairs and Forestry
completed a comprehensive Reserve Determination study for the Thukela River. Upon
reviewing the results it was clear that many of the variables assessed were of low
confidence or there was not sufficient data collected within the region of the Mandini
and Thukela River confluence and further downstream (Resource Unit K). Therefore
the previous studies were not able to determine the degree to which the industries in
the lower Thukela system impacted upon the integrity of the system. The aim of this
study was therefore to assess the contributing impacts of the Tugela pulp and paper
mill and other industrial activities on the ecological integrity of the lower Thukela River.
This was done by through a toxicity assessment of the potential impacts of effluent and
wastewater using the Direct Estimation of Ecological Effect Potential (DEEEP)
methodologies. The toxicity of pulp and paper effluent from the Thukela mill and the
receiving water body was compared to effluents from two other mills (Stanger and
Ngodwana), assessing the water quality in relation to the input of different industrial
effluents in the lower Thukela River. The general integrity of the lower Thukela River in
relation to the input of different industrial effluents was assessed using the Habitat
Quality Index (HQI), Habitat Assessment Index (HAI), macroinvertebrate and fish
population studies. These studies were integrated to derive the Ecostatus of the lower
Thukela River using the Macro-invertebrate and Fish Response Assessment Indices
(MIRAI and FAII respectively).
The toxicity testing (DEEEP) showed the paper mill effluent in the Mandini River was
the least hazardous whilst Ngodwana effluent showed the highest potential to elicit a
harmful impact on the receiving water body. The latter effluent displayed the highest
LC50 values for the fish and the Daphnia toxicity tests, as well as an extremely high
base-pair substitution mutagen activity. Toxicity was also found in algae at 100% raw
effluent exposure. Tugela and Stanger mill effluent samples were very similar in their
toxicity, except that Stanger effluent showed greater mutagenicity potential with
exceptionally high values of revertants. The Tugela effluent samples showed no
concerning levels of mutagenicity. The fish showed lower levels of response to the
Tugela sample when compared to the Stanger sample. Thus comparatively the
Thukela system is regarded to be the least at risk with regards to effluent discharge
into the receiving water body.
The lower Thukela River integrity assessment showed a sharp increase in temperature
below the discharge point of the pulp and paper mill effluent. This was attributed to the
excessive temperatures recorded in the pulp and paper effluent itself. There was
further decrease in dissolved oxygen, which was due a combination of the industrial
waste water in the Mandini River and the pulp and paper effluent.
The increased organic content in the sediments of the lowest site situated downstream
(TR5) is a combination of both reduced velocity of the stream flow entering the upper
reaches of the estuary as well as increased organic material entering the river via the
pulp and paper effluent and the Mandini River above TR3-D. This was accompanied by
increased contribution of fine particle size sediments to the overall sediment
composition.
Habitat conditions were near natural at sites upstream of the Mandini River and
effluent discharge confluences with the Thukela River. The exception was at TR1 as
the weir results in unnatural inundation of biotopes upstream. The habitat conditions
around the confluences of the Mandini River and pulp and paper mill effluent discharge
are diminished with a recovery noted further downstream at TR4 and TR5.
Invertebrate assessment shows the upstream sites to be natural, while the impact sites
were largely to seriously modified. Once again the downstream sites (TR4 and TR5)
show an improvement to recover to a moderately modified state. The fish assessment
also shows a decrease in the FAII score below the impacts when compared to the
integrity above the impacts. However these results are of low confidence due to
insufficient sampling effort as only electronarcosis, seine and cast nets were used.
The Ecoclassification assessment indicated a clear decrease in Ecostatus between the
sites that are upstream of the impacts caused by the industrial effluent from the
Mandini River and the pulp and paper mill effluent from the effluent discharge stream.
The MIRAI also clearly indicated that the major impacts are caused by the combination
of the Mandini River and the pulp and paper effluent. However there was a recovery in
the river further downstream from the impacts.